In the existing arts, U.S. Pat. No. RE36703E discloses a coding system for multiple transmitters and a single receiver for a garage door opener, and U.S. Pat. No. 4,750,118 also discloses such a coding system prior to the former. For controlling the position of the barrier (door), a garage door opener comprises components below. At least one radio frequency transmitter has a non-user changeable code for radio frequency transmitting a radio frequency transmission. A radio frequency receiver is adapted to receive the first-mentioned radio frequency transmission from the first-mentioned radio frequency transmitter and to receive a second radio frequency transmission from a second radio frequency transmitter having a second non-user changeable code, different from the first non-user changeable code. A program mode designator is adapted for designating a program mode. A memory comprises a plurality of storage location. A processor has a processor controlled code location pointer and is responsive to a program mode designation by the program mode designator and the reception by the radio frequency receiver of the first-mentioned radio frequency transmission for storing a first stored code corresponding to the first-mentioned radio frequency transmitter in one of the plurality of storage locations derived from the processor controlled code location pointer. The processor is responsive to the program mode designation by the program mode designator and the reception by the receiver of the second radio frequency transmission for storing a second stored code corresponding to the second radio frequency transmitter in another of the plurality of storage locations derived from the processor controlled code location pointer. The processor is responsive to an operate mode and the reception of the first-mentioned radio frequency transmission after the storage of the first stored code for moving the barrier and responsive to the operate mode and to the reception of the second radio frequency transmission after the storage of the first and the second stored codes for moving the barrier. Because the garage door opener puts the codes in one memory, when the radio frequency transmitter is lost and needs to be replaced by a new one, the program mode designator designates a program mode and each radio frequency transmitter transmits a program signal to make the memory memorially program. But under the program mode, a code signal transmitted by an unlawful radio frequency transmitter may also be memorially programmed by the memory, and so the unlawful radio transmitter can open the garage door so that the garage door opener is unsafe in use.